Delivery system having a rapid pusher assembly for self-expanding stent, and stent exchange configuration

ABSTRACT

A pusher assembly for a delivery system for a sell-expanding stent ( 6 ) which is delivered by proximal withdrawal of a sheath ( 4 ) radially surrounding the stent has a stent pusher element ( 8 ) which defines a lumen for a guidewire ( 2 ), a pusher strand ( 16 ) that extends to the proximal end of the delivery system and bears an end-wise compressive stress during release of the stent. A transfer shaft ( 12 ) links the distal end of the pusher strand ( 16 ) to the pusher element ( 8 ) and lies side-by-side with the guidewire ( 2 ). In a rapid exchange version, an adapter ( 20 ) provides two lumens side-by-side, one ( 22 ) carrying the pusher strand ( 16 ) and the other ( 14 ) defining a proximal guidewire part. To the adapter is mounted the proximal end of the stent sheath ( 4 ). The system allows modular ( 14 ) construction, a tapered tip ( 4 A) on the sheath, and an uncluttered internal configuration which facilitates passage of pulses (F) of liquids from the proximal to the distal end of the system.

TECHNICAL FIELD

[0001] This invention relates to a stent pusher assembly, and to adelivery system having a rapid-exchange configuration for deploying aself-expanding stent at a stenting site within a human or animal body.

BACKGROUND ART

[0002] EP-A-1 095 634 (EP 634) discloses all features of the preamble ofindependent claims 1 and 11. EP 634 discloses a system in which the softatraumatic distal tip of the system is at the leading end of the innercatheter. The outer sheath of the delivery system has a distal end whichstops proximally short of the atraumatic tip.

[0003] Stents to be deployed at a stenting site within a human or animalbody expand radially in the course of delivery, from a radially compactdelivery disposition to a radially larger deployed disposition. Inself-expanding stents made of stainless steel, the deformation of thestent is below the elastic limit, the stent until its deployment beingradially confined and under elastic stress and typically released byproximal withdrawal of a confining sheath while the stent is itselfprevented from moving proximally with the confining sheath by abutmentwith a stop on the distal end of a catheter shaft which suffers axialcompressive stress while the surrounding sheath is proximally withdrawn.

[0004] By contrast, stainless steel stents which are relaxed in aradially compact disposition suffer plastic deformation when expandedinto their deployed disposition by inflation of a balloon within thelumen of the stent.

[0005] An early example of stainless steel self-expanding stents isGianturco U.S. Pat. No. 4,580,568 and an early example of the balloonexpansible stainless stent is Palmaz EP-A-221 570.

[0006] A third category of stent is the memory metal stent, made of abiologically compatible nickel-titanium shape memory alloy withmartensitic and austenitic phases. At body temperature, the stent“seeks” to revert to the austenitic phase. Typically it is confinedwithin a surrounding sheath and again released at the stenting site byproximal withdrawal of this sheath.

[0007] The present invention offers improvements in systems to deliverthose stents which are brought to the stenting site within a confiningsurrounding sheath.

[0008] In the technical field of stenting, there is a desire to reducethe transverse dimensions of the stent delivery system. In this field,the widely used measure of transverse cross-section is the unit of“French”, often abbreviated to “F” which is a one third part of amillimeter. Thus, a 6F (six French) delivery system has a diameter of 2millimeters.

[0009] For any particular stenting operation, one has to select aparticular stent and a particular delivery system. There is a largechoice in both of these elements. Accordingly, it would be an advantagefor manufacturers of stents and their delivery systems to achieve adegree of modularity in the design and construction of stents and theirdelivery systems. For example, there is a wide range of stents whichcould be delivered by a six French delivery system and it wouldtherefore be convenient for the manufacturer of a stent delivery systemto be able to tailor a basic six French system to fit any particularstent which would be compatible with a six French delivery system. Thiswould reduce costs, to the advantage of patients, while retaining fullflexibility for medical practitioners to optimise their choice of stentfor any particular patient.

[0010] Like many catheter systems, a stent delivery system is often usedwith a flexible guidewire. The guidewire is preferably made of metal,and is slidably inserted along the desired body passage. The deliverysystem is then advanced over the thus pre-placed guidewire by“backloading” or inserting the proximal end of the guidewire into adistal guidewire port leading to a guidewire lumen defined by thedelivery system.

[0011] Many conventional delivery systems define guidewire lumens thatextend along the entire length of the outer sheath. These deliverysystems are described as “over-the-wire” delivery systems, in that thedelivery system is guided to the site of the stenosis over theguidewire, the guidewire thereby exiting the delivery system at theproximal end of the delivery system. “Over-the-wire” delivery systemsprovide several advantages, including improved trackability, the abilityto flush the guidewire lumen while the delivery system is inside thepatient's body, and easy removal and exchange of the guidewire while thedelivery system remains in a desired position in the patient.

[0012] In some circumstances, however, it may be desirable to provide a“rapid exchange” delivery system, which offers the ability more easilyto remove and exchange the delivery system while retaining the guidewirein a desired position within the patient. In a rapid-exchange deliverysystem, the guidewire occupies a lumen located only in the distalportion of the delivery system. The guidewire exits the delivery systemthrough a proximal guidewire port, closer to the distal end of thedelivery system than to its proximal end, extends in parallel along theoutside of the proximal portion of the delivery system.

[0013] Because a substantial length of the guidewire is outside thedelivery system, it may be manually held in place close to the pointwhere it passes the entry point on the body of the patient, as thedelivery system is removed. This facilitates handling, removal andexchange of the delivery system for the practitioner for the followingreasons.

[0014] With a guidewire lumen that is much shorter than the fullcatheter length a single physician can insert and remove a stentdelivery system into and from the patient's body. Whereas conventionaldelivery systems require a guidewire having a length at least double thelength of the outer catheter, the rapid-exchange configuration allowsthe use of much shorter guidewires which enable a single physician tohandle the proximal end of the guidewire at the same time as thecatheter at the point of its entry into the body of the patient.

[0015] Accordingly, the present invention advantageously provides astent delivery system having a rapid-exchange configuration fordelivering and deploying a self-expanding stent.

[0016] Stents themselves cannot be directly seen during their journey tothe stenting site, nor can one directly see whether the stent is exactlylocated as desired within the stenting site. Rather, indirect means haveto be used to follow the progress of the stent through the body and makesure that it is correctly located before it is deployed. Thus, a stentdelivery system is used during deployment to carry radiopaque contrastor marker fluid to the stenting site so that the target stenosis can beseen through the reduced amount of radiopaque fluid in the bodily lumenat the stenosis. This radiopaque fluid is generally injected through aninjection port at the proximal end of the delivery system and through anannular space between an outer sheath of the delivery system and aproximal portion of an inner catheter shaft. The visibility of thestenosis is adversely affected when the lumen, through which radiopaquecontrast fluid is injected, is too small to deliver a strong pulse ofcontrast fluid. As pulses of fluid are used for visualisation, theeffectiveness of visualisation depends on the volume flow in each pulse.This in turn depends on the ease of flow of the fluid along the fulllength of the delivery system, from the point of injection at theproximal end, to the stenosis beyond the distal end of the deliverysystem.

[0017] Thus, delivery systems which offer a large cross-section andunimpeded lumen for contrast fluid will be favoured by radiologists,other things being equal. The visibility can additionally be increasedby further reducing the resistance of the system to pulses of contrastfluid. It is therefore an object of the present invention to providegood visualisation with contrast fluid, without sacrifice of otherimportant performance aspects of the delivery system, includingpushability and low overall diameter. By increasing “pushability” wemean the capability to be advanced longer distances along narrower andmore tortuous bodily lumens.

[0018] Furthermore, the delivery system invariably carries at least oneradiopaque marker at a known location relative to the length of thestent, so that radiologists can be sure of the location of the ends ofthe stent, on the basis of their knowledge of the location of theradiopaque marker. Even if the stent is rendered sufficiently radiopaquefor it to be seen, it is still useful to have a radiopaque marker on thedistal end of the delivery system, to reveal successful separation ofthe stent from the delivery system.

[0019] Thus, in our example of a six French delivery system, to be usedfor delivering stents of various lengths, there will be a wish toprovide radiopaque markers within the delivery system at twospaced-apart locations on the axis of the delivery system, correspondingto the opposite ends of the stent (until the stent is deployed out ofthe system). One object of the present invention is to offer a degree ofmodularity in this design aspect.

[0020] With delivery systems having a rapid-exchange configuration, justas with over-the-wire systems, the stent delivery system is advancedover the guidewire, itself normally within a guide catheter, in order tobring the distal tip and stent to the stenting site. Depending on theapplication, different diameter guidewires are specified. Two commonlyused guidewire diameters are 0.46 mm/0.018 inches and 0.89 mm/0.035inches (commonly known as 18 thou or 35 thou guidewires). Thus, afurther degree of modularity can be achieved by offering a deliverysystem which is compatible with a range of guidewire diameters,specifically, both 18 thou and 35 thou guidewires.

[0021] Naturally, it would be an advantage for any new stent deliverysystem to be able straightforwardly to take the place of those previousdelivery systems which individual practitioners have grown to becomfortable using. One such system uses in its proximal portion ametallic rod, which can be either solid or hollow, made of stainlesssteel.

[0022] Further, it goes almost without saying, that good design forstent delivery systems is indicated by manufacturing steps which can beperformed with high precision and reliability, yet with acceptable costlevels. This is yet another objective of the present invention.

[0023] Finally, for any system which is extremely long in proportion toits diameter, and features at least three co-axial elements, thecylindrical surfaces of these co-axial elements need to be so composedand conformed that friction between them is low enough that the co-axialelements can be moved tolerably easily axially relative to each other.It is yet another object of the present invention to provide systemswhich offer possibilities for bringing these friction levels down toadvantageously low levels.

[0024] Along with all these issues already appreciated by those skilledin the art, there is a further performance aspect which becomes evidentwhen a self-expanding stent is released progressively by successiveproximal stepwise movements of the outer confining sheath.

[0025] Typically, the delivery system is extremely long in proportion toits cross-sectional dimensions, and is constructed predominantly orwholly from synthetic polymeric materials which have substantialelasticity and marked kinetic aspects to their deformationcharacteristics. In such a case, any particular rate of strain imposedon the proximal end of the outer sheath is likely to be experienced atthe distal end of the same sheath in a somewhat different strain rate.For example, a fast squeeze of the trigger of a deployment system at theproximal end of the sheath will likely result in a somewhat slowerresulting proximal advancement of the distal end of the same sheath.Furthermore, a pull on the sheath will impose compressive stresses alongthe length of the inner shaft, likely leading to a proximal movement ofthe stent which then relaxes back to the original, more distal, positionof the stent as the tensile stress in the outer sheath eases backtowards zero. In its own delivery systems, present applicant hasobserved what happens at the distal end of a stent delivery systemduring successive squeezes of the trigger of a delivery system whichpulls the outer sheath proximally in a series of steps. The appearanceat the stent end of the system is as if the system were “breathing” inthat it, and the stent, moves axially first proximally, then distally,with each squeeze of the trigger.

[0026] This “breathing” phenomenon is of course a complicating factorwhen it comes to precision of placement of the stent within anyparticular stenting site. It is yet another object of the presentinvention to ameliorate this problem.

SUMMARY OF THE INVENTION

[0027] These and other objects are solved by a stent deployment systemwhich shows the features of claim 1 below, including an annular pusherelement which abuts the stent to stop it moving proximally when theouter sheath is withdrawn proximally to release the stent.

[0028] Preferred embodiments of the present invention are described independent claims.

[0029] According to one aspect of the present invention there isprovided a pusher assembly for a delivery system for a self-expandingstent, the pusher assembly constituting a catheter shaft with a proximalpusher end to receive an end-wise compressive force and a distal pusherend to deliver said force to a stent to be delivered, the pusherassembly comprising a pusher strand extending from the proximal pusherend to a distal strand end which is nearer the distal pusher end thanthe proximal pusher end; a pusher element which abuts the stent in useto deliver said force to the stent; and a transfer shaft having aproximal and a distal end, the proximal end being connected to thedistal tube end and the distal end being connected to the pusher elementand characterised in that the pusher element defines a guidewire path,and the transfer shaft lies to one side of said path.

[0030] By contrast, in conventional systems such as that of EP 634 inwhich the atraumatic tip is carried on the inner catheter, the pusherelement is mounted on a tube which has a guidewire lumen and extendsdistally all the way to the tip.

[0031] According to another aspect of the present invention, defined inclaim 11 below, there is provided a stent delivery system having a rapidexchange configuration for a self-expanding stent which providesimproved visualisation through an increased volume flow in each pulse.The volume flow in each pulse is increased in the present invention dueto a simplified and reduced internal structure of the delivery system.

[0032] The scheme of the stent delivery system of Gianturco U.S. Pat.No. 4,580,568 is represented herein by accompanying drawing FIG. 1.Referring to FIG. 1, the essential features of a basic delivery systemare an outer sheath 4 confining the stent 6 in a radially compressedstate and a pusher element 8 preventing proximal movement of the stentwhen the outer sheath 4 is proximally withdrawn. The pusher element iscarried on an inner catheter shaft 3. Here, the delivery system isinserted over a guidewire 2 into a lumen of a human or animal body.

[0033] The present invention recovers much of the simple deliveryconcept of FIG. 1 by shortening the inner catheter shaft so that itsdistal end is relatively close to the proximal guidewire lumen exitport. In by now conventional delivery systems, the inner catheter shaft3 extends beyond the distal end of the stent 6 to provide a tapered tip,for ease of insertion of the delivery system into the patient's body andfor reducing trauma whenever the catheter is advanced distally.Above-mentioned EPO 634 discloses a stent delivery system which conformsto this conventional model.

[0034] In the present invention, using the pusher element to define atleast a short distal guidewire lumen, and providing the system tip taperon the distal end of the outer sheath, renders redundant an innercatheter within the stent and distal of the stent. Therefore, theinternal structure of the delivery system is more open, whichconsequently enhances ease of flow and the volume of contrast fluid thatcan be ejected from the distal end of the delivery system with eachsuccessive pulse imposed from the proximal end of the delivery system.Hence, visualisation is improved.

[0035] Secondly, the manufacturing and assembling steps required to getthe delivery system of the present invention ready for use are minimiseddue to the simplified internal structure. There exists no longer theneed for keeping the stent at a fixed position on the inner cathetershaft while the outer sheath is fitted over the stent. Also, the risk ofadvancing the stent too far distally and out of the distal opening ofthe outer sheath during assembly of the delivery system is minimised,since the outer sheath in the present invention comprises the taperedtip which acts as a distal stopper for the stent during assembly. Also,it is worthwhile to note that there are fewer steps during manufacturingand assembly of the stent delivery system, which itself is a valuablegain in this technical field.

[0036] The introduction of a stent using the stent delivery system ofthe present invention, and subsequent removal of the delivery system, isfacilitated especially in tortuous vessels and other body lumens havinga relatively narrow diameter because, once the stent has been placed ata desired site inside the patient's body, there need be no component ofthe delivery system which is radially inwardly located from the stentand which has to be proximally withdrawn through the stent lumen.Especially in narrow and sharply curved body vessels, this mightintroduce a risk that the distal tip being withdrawn through the stentlumen interferes with bodily tissue protruding radially inwardly throughthe interstices of the stent and into the stent lumen. The deliverysystem of the present invention avoids this problem by providing thetapered tip on the distal end of the outer sheath so that, duringremoval of the delivery system out of the patient's body, there need beno system components which travel proximally within the stent lumen andare likely to engage with the inner surface of the stent.

[0037] In one preferred embodiment, the pusher element is a cylinderwhich has a distal-facing end face at the distal end of the cylinder topush on the proximal end of the stent. Thus, the end face will likely beflat and transverse to the axis of the cylinder. The pusher element canserve as, and preferably does serve as, a radiopaque marker.

[0038] If desired, the pusher element can also serve as a mount for adistal marker carrier tube cantilevered distally forward from the pusherelement to lie within the space that will correspond to the lumen of thestent to be deployed by the system. This is useful when it is requiredto have on the delivery system a radiopaque marker for the distal end ofthe stent. This radiopaque marker can be placed on the carrier tube at aposition at or towards the distal end of the carrier tube andcorresponding to the distal end of the stent. For stents of differentlengths, the length of the carrier tube can easily be varied tocorrespond to the stent length, prior to fixing the distal marker on thecarrier tube.

[0039] It will be appreciated that the carrier tube requires relativelylittle strength, so can be made thin and flexible, thereby reducing therisk of its interfering with tissue protruding through the stent duringits withdrawal from the stenting site.

[0040] As the carrier tube is a relatively simple and isolated part ofthe delivery system, and conveniently made of a synthetic polymericmaterial, it will be a relatively simple matter to change the length ofthe carrier tube to suit any particular stent destined to be carried onthe system. If desired, the carrier tube can be extended backwardlyproximally from the pusher element and given a bell end or flared endoutwardly proximally. This flared end provides security against thepossibility of unwanted distal slippage of the carrier tube distallythrough the pusher element and of being left behind in the body when thedelivery system is withdrawn. It may also be useful to guide theguidewire through the system whenever there is need to introduce thedistal end of the guidewire from the proximal end of the system.

[0041] Another option for modularisation is given by a transfer shaftconnecting the rod or inner catheter with the pusher element. This canbe set to any desired length, to accommodate stents of different lengthin a delivery system which features standard length catheter componentssuch as the sheath, rod or inner catheter and pusher tube. It may beconvenient to use a welded joint to fasten one or both of the two endsof the transfer shaft to the pusher element and rod, respectively.

[0042] For a better understanding of the present invention, and to showmore clearly how the same can be carried into effect, reference will nowbe made, by way of example, to the accompanying drawings of embodimentsof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 shows in longitudinal axial section the distal portion of aprior art delivery system;

[0044]FIG. 2 is a cross-section of the distal portion of a deliverysystem having a rapid-exchange configuration in accordance with apreferred embodiment of the present invention;

[0045]FIG. 3 shows an isometric view of the adapter having two lumenseffecting the rapid exchange configuration;

[0046]FIG. 4 shows a cross-section of the proximal portion of thedelivery system, the pull-back device used to proximally retract theouter sheath, in accordance with a preferred embodiment of the presentinvention;

[0047]FIG. 5 shows a cross-sectional view of the distal portion of anover-the-wire pusher assembly according to a second embodiment of theinvention;

[0048]FIG. 6 shows a cross-sectional view of the distal portion ofanother over-the-wire pusher assembly according to a third embodiment ofthe invention;

[0049]FIG. 7 shows a cross-sectional view of the distal portion of yetanother over-the-wire assembly, being a fourth embodiment of theinvention;

[0050]FIG. 8 shows at larger scale the distal tip portion of the FIG. 7embodiment; and

[0051]FIG. 9 shows at the scale of FIG. 8 a part of the FIG. 7 distalportion which is proximal of the tip shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] The following description of the preferred embodiments of thepresent invention is merely illustrative in nature, and as such does notlimit in any way the present invention, its application, or uses.

[0053]FIG. 2 shows a cross-section of the distal portion of a deliverysystem having a rapid-exchange configuration in accordance with apreferred embodiment of the present invention.

[0054] In FIG. 2, a guidewire 2 extends beyond the distal end of thedistal portion of the delivery system along which the stent deliverysystem is advanced to the site of the stenosis inside the patient'sbody. The stent 6 is held in a radially compressed state by means of anouter sheath 4 the distal end of which constitutes the distal end of thestent delivery system. The distal tip 4A of the outer sheath 4, as shownin FIG. 2, is tapered in order to facilitate advance of the stentdelivery system along a bodily lumen. Furthermore, the outer sheath 4comprises a radiopaque marker 27 the position of which is indicative forthe distal end of the stent until deployment of the stent. The guidewire2 extends all the way through the outer sheath lumen and exits thedistal portion of the stent delivery system at a proximal guidewire port24.

[0055] A pusher element 8 abutting the stent 6 in use of the deliverysystem prevents proximal movement of the stent 6 when the outer sheath 4is withdrawn proximally to release the stent. The pusher element 8,which at the same time serves as a proximal radiopaque marker, isconnected to a transfer shaft 12. The pusher element 8 is preferablylaser-welded to the distal end of the transfer shaft 12. For ease ofconnection the distal end of the transfer shaft 12 is tapered andembedded in a respective slot provided in the proximal end of the pusherelement 8. The distal end of the transfer shaft 12 is tapered, and thetransfer shaft 12 is corresponding oblate at its distal end, so that thedistal end of the transfer shaft 12 can be fitted into a respective slotof the adjacent pusher element 8, with the circumferential surface overa specific arc length of the oblated end being flush with thecircumferential surface of the pusher element 8. The slot provided inthe proximal end of the pusher element 8 has an axial length whichextends from the proximal end of the pusher element 8 beyond midwayalong the axial length of the pusher element 8. This ensures asufficiently rigid connection of the transfer shaft 12 with the pusherelement 8. Such shaping of the distal end of the transfer shaft 12 andthe pusher element 8 optimises the flow of injected contrast fluid F,since the fluid does not meet any unnecessary barrier when travellingalong the length of the transfer shaft 12. In this way, the flowresistance of the injected contrast fluid F is minimised.

[0056] The transfer shaft 12 is capable of receiving an endwisecompressive force C and transmitting the force C to the proximal end ofthe stent 6, thereby preventing proximal movement of the stent 6 whenthe outer sheath 4 is withdrawn proximally by imposition of tensileforce T on the sheath 4. The arrows in FIG. 2 are indicative for thedirection of the respective forces T and C.

[0057] A connection piece 14, such as a tube, at the proximal end of thetransfer shaft 12, as shown in FIG. 2, enables the accommodation ofdifferent stent lengths in an unchanged sheath 4 by an appropriateadjustment in the length of the transfer shaft 12 in accordance with thelength of the respective stent 6.

[0058] The cut-to-length transfer shaft end within the connection tube14 is glued or soldered to the connection tube 14. The proximal end ofthe transfer shaft 12 is directly connected to the distal end of the rod16 by means of a solder joint or glue. Otherwise, the connection tube 14can be no more than a collar into which two adjacent ends of separatetransfer shaft portions are inserted end-to-end and approximated, suchthat both abutting ends of the transfer shaft 12 portions are inphysical contact with each other inside the collar. Therefore, there isno relative axial movement of the two adjacent ends of the transfershaft 12 portions within the collar. Thus, the longitudinal forcetransmission between the proximal end of the tube 16 receiving theendwise compressive force C to the proximal end of the stent 6 isoptimised.

[0059] The proximal end of the distal portion of the stent deliverysystem, as shown in FIG. 2, comprises an adaptor 20 having two lumens22, 24 for effecting the rapid-exchange configuration. The guidewire 2exits the distal portion of the stent delivery system through aguidewire port 24 of the adaptor 20, so as to be exposed outside thestent confining sheath 4 to enable the rapid exchange. The guidewireport 24 is preferably off-centre of the adapter 20. The orifice of thesecond lumen 22 is defined by a pipe 18.

[0060] Referring to FIG. 2, a rod 16 being part of the pusher assemblyand preferably made of metal abuts at a distal end thereof the proximalend of the transfer shaft 12 inside the connection piece 14. Itsproximal end extends beyond the proximal end of the pipe 18. The rod 16extends distally from the distal portion of the delivery system throughthe second lumen 22 of the adapter. At its proximal end it receives theendwise compressive force C.

[0061] In a further embodiment of the present invention, not shown, therod 16 can be provided as a tube with a lumen running from the proximalend of the system to the lumen of the pipe 18.

[0062] In both embodiments, the pipe 18 is connected to the adaptor 20and furthermore, the adaptor 20 is connected to the outer sheath 4. Theintegrity of this connection is somewhat crucial for the properfunctioning of the delivery system, since the outer sheath 4 is usuallymade of a polymeric material whereas the adaptor 20, the rod 16 (ortube), and the transfer shaft 12 are preferably made of metal, such asstainless steel. Metal-to-polymer connections are normally made by meansof an adhesive.

[0063] To permit sufficient rigidity and to provide a rupture-resistantconnection of the pipe 18 through the adaptor 20 to the outer sheath 4,the pipe 18 is advantageously welded into a recess of the adaptor 20.Tension studs 20A, as shown in FIG. 3, are provided in the proximity ofthe distal end of the adapter 20 to engage along the entirecircumference of the adapter 20 with individual strands of a braid 43encapsulated by the polymeric material of the outer sheath 4. Thetension studs 20A protrude radially outwardly into the interstices ofthe braid 43 to reduce the dependence on glue to prevent rupture of theconnection between the adapter 20 and the outer sheath 4. The stud tobraid link between the pipe 18 and the outer sheath 4 via the adapter 20feature metal all the way from one end of the system to the other sothat the risk that the adhesive joint between the adapter 20 and theouter sheath 4 may break is reduced and the strain suffered by thesystem in releasing a stent is also kept small. Other type ofconnections will be apparent to those skilled in the art and an explicitexplanation thereof is therefore omitted.

[0064] When using the stent delivery system, a tensile force T acts onthe pipe 18, thereby proximally displacing the outer sheath 4 to releasethe stent 6, and at the same time a compressive force C is received bythe tube or the rod 16 at its proximal end and is transmitted to thetransfer shaft 12 in order to prevent proximal displacement of the stent6 during stent deployment.

[0065] Since the pusher element 8 provides a lumen for the guidewire,abuts the stent 6 in use and is supported axially by the transfer shaft12, and since the stent 6 is self-expanding and so is pressing radiallyoutwardly on the sheath 4, there is no need for an inner catheter toextend beyond the proximal end of the stent 6. The tapered tip 4A of thesheath 4 facilitates advance of the catheter system through a tortuouslumen of the patient's body. The tapered tip 4A also resists inadvertentor premature distal movement of the stent 6 relative to the sheath 4,such as when the delivery system is introduced into a narrow vesselinside the patient's body. In this way, the tapered tip 4A of the outersheath 4 can act a distal stopper for the stent.

[0066] For a detailed description of such tapered tips and their use,see Applicant's WO 01/34061.

[0067] A distal marker carrier 10, itself carried on the pusher element8, exhibits a length sufficient to project distally beyond the stent 6and defines a lumen for the guidewire 2. In use, the guidewire 2 extendsalong an axial path which lies side by side with the transfer shaft 12,which shaft 12 is off the axis of the outer sheath 4. The proximal endof the distal marker carrier 10 is attached, conveniently by glue, tothe inner surface of the pusher element 8 to fix its axial position. Theproximal end of the distal marker carrier 10 has a flared end or showssome sort of tulip-shape which facilitates distal advancement of theguidewire 2 through the pusher assembly of the delivery system. Thefixing established by the glue and the flared ends also reduces thelikelihood of separation of the carrier tube 10 from the pusher element8.

[0068] The distal marker carrier 10 carries a distal marker 26, such asa radiopaque marker, indicating the position of the distal end of thestent 6. The inner surface of the distal marker 26 is flush with theinner surface of the distal marker carrier 10 for undisturbed elativeaxial movement of the guidewire 2. Preferably, a particular heattreatment is employed to attach the distal marker 26 to the distalmarker carrier 10, so that the distal marker is partially fused togetherwith the distal marker carrier 10. It is also conceivable to embed orswage the distal marker 26 into the distal marker carrier 10 because thematerial used for the distal marker carrier 10 is relatively soft,preferably a resin tube.

[0069] The distal marker carrier 10 is a polymeric tube whereas thepusher element 8, the transfer shaft 12, and rod 16 or tube 16 are madeof metal, conveniently stainless steel. It is also conceivable to useother material combinations for these parts, such as nickel titaniumshape memory alloy for the transfer shaft 12 and a composition ofplatinum/iridium (90/10) for the pusher element 8.

[0070] The outer sheath 4 may also carry a marker band such as one 27 onits inner luminal surface just proximal of its tapered tip 4A formarking the distal end of the outer sheath 4.

[0071] Some applications require a thicker guidewire 2, such as a 35thou guidewire. In such cases, one may choose to omit the distal markercarrier 10. Otherwise, one may choose to locate the marker 26 distal ofthe distal end of the stent in the free volume 40 between the stent andthe tip 4A, thereby minimising the consumption of lumen cross-sectioninside the stent lumen. The remaining structure of the pusher assemblycan remain the same. Hence the versatility of the pusher assembly isincreased because of its usefulness with guidewires of differentdiameters.

[0072]FIG. 3 shows an isometric view of the adapter 20, preferably madeof metal, such as stainless steel, effecting the rapid exchangeconfiguration. The adapter comprises two lumens 22, 24 one of which is aguidewire lumen 22 and the other one of which permits the rod 16 or tubeto exit the adapter. Lumen 24 of the adapter is defined by two opposingarcuate segments 23A and 23B. The pipe 18 is introduced into lumen 24 ofthe adapter 20 from the proximal end of the adapter which has the shapeof a mushroom until it abuts the distal end of a recess (not shown). Inthis manner, the adapter does not need to have a circumferential sidewall which encloses lumen 24 by 360°. Hence, the lateral dimensions areminimised. Furthermore, as shown in FIG. 3, tension pins (studs) 20A areprovided on the outer circumferential surface of the distal portion ofthe adapter 20 engaging with the braid 43 which is encapsulated by thepolymeric material of the outer sheath 4. Lumen 24 which is a guidewirelumen is located off-centre of the adapter 20 and allows the guidewire 2to exit the delivery system to effect the rapid-exchange configuration.The adapter is preferably made of metal, such as stainless steel, butthe use of other alloys is conceivable.

[0073] Referring now to FIG. 4, a cross-sectional view of the proximalportion of the stent delivery system is shown. The proximal portion ispart of a pull-back device used for proximally retracting the outersheath 4 to release the stent 6. The pipe 18 which is connected to thesheath 4 via the adapter 20 is linked to an adapter ring 36. A weldedjoint is preferably be used for the link but other types of joints maybe used, such as glue or an interference fit etc. The adapter ring 36 isjoint to a polymeric sleeve 38 fitted into the distal portion of adistal hub 40. As the distal hub is successively pulled back proximallywith every squeeze on the trigger of the pull-back device (not shown), aproximal hub 46 at the proximal end of the rod 16 or tube is heldstationary at the same time by a compressive force being transmittedfrom the proximal hub 46 via rod 16 and transfer shaft 12 to the pusherelement 8. In this way, controlled release of the stent at a desiredposition inside the patient's body is achieved.

[0074] The proximal portion of the stent delivery system furtherprovides the possibility to insert contrast fluid through theLuer-adapter 42 into the annulus between the distal hub 40 and asupporting member 44 being sealed by an O-ring 48 and connected to rod16. The contrast fluid passes beyond the distal end of the distal hub40, creeps through the gap between the adapter ring 36 and the rod 16and emerges from the distal end of the pipe 18 finally to reach thedistal end of the outer sheath 4 to get squirted out into the vessel ofthe patient's body.

[0075] The Luer-valve assembly 42 also comprises a safety lock forlocking the axial movement of rod 16, (the subject of Applicant'sPCT/EP02/06782 and earlier British Patent Application No. 0114939.2),which ensures safe transport of the packaged delivery system without therisk of inadvertent release of the stent and to enable the physician tointerrupt the stent deployment process, when needed, without having tobe concerned with the displacement of the stent whilst the physician isnot holding the delivery system in his/her hands.

[0076] The pusher assembly, as shown in FIG. 5, is destined to be usedfor an 18 thou guidewire 20. The entire pusher assembly is enclosed byan outer catheter 4 of an over-the-wire stent delivery system prior todeployment of the stent 6. In this condition the stent 6 is held in aradially compressed configuration by the same outer catheter 4. Fordeployment of the stent 6, the outer catheter 4 is withdrawn until thedistal tip 63 is proximal of the proximal end of the stent 6.

[0077] The pusher assembly incorporates a catheter shaft 66, the distalend of which is connected to a transfer shaft 64. A pusher element 68 isconnected to the distal end of the transfer shaft 64. During the courseof stent deployment the distal end 69 of the pusher element 68 abuts theproximal end of the stent 6. Thus, the pusher element 68 serves as astop for the stent 6 during stent deployment, to prevent proximalmovement of the stent as the outer catheter 4 is withdrawn proximally.

[0078] The proximal end of the pusher element 68 is laser-welded to thedistal end of the transfer shaft 64 and the same manner of connection isused for connecting the proximal end of the transfer shaft 64 to thedistal end of the catheter shaft 66.

[0079] For ease of connection, both the distal and the proximal ends ofthe transfer shaft are tapered and embedded in respective slots providedin the proximal end of the pusher element 6 and the distal end of thecatheter shaft 66. The ends of the transfer shaft 64 are tapered suchthat the circular cross-section of the transfer shaft 64 between itsends is oblate at its ends, so that both ends can be fitted intorespective slots of the adjacent pusher element 68 and catheter shaft66, with the circumferential surfaces over a specific arc length of bothoblated ends being flush with the circumferential surface of the pusherelement 68 and the catheter shaft. The slot provided in the proximal endof the pusher element 68 has an axial length which extends from theproximal end of the pusher element beyond mid-way along the axial lengthof the pusher element 68. The length of the slot in the distal end ofthe catheter shaft 66 is much the same length, and long enough to ensurethat a sufficient connection between the transfer shaft 64 and thecatheter shaft 66 is obtained. Such shaping of the two ends of thetransfer shaft and the pusher element 68 and the catheter shaft 66maximises the flow of injected contrast fluid, since the fluid does notmeet any unnecessary barrier when travelling along the length of thetransfer shaft. In other words, the resistance to the flow of theinjected contrast fluid is minimised.

[0080] A connection piece such as a tube 78 at an intermediate positionof the transfer shaft 64 enables the accommodation of different stentlengths in an unchanged sheath 4 and catheter shaft 66, by anappropriate adjustment in the length of the transfer shaft portions inaccordance with the length of the respective stent. The twocut-to-length transfer shaft portion ends bridged by the connection tube78 are either glued or soldered to the connection tube 78. Theconnection tube 78 can be no more than a collar into which the twoadjacent ends of the separate transfer shaft portions are inserted andapproximated, such that both ends of the transfer shaft are in physicalcontact with each other inside the collar. Therefore, there is norelative axial movement of the two adjacent ends of the transfer shaftportions within the collar.

[0081] A distal marker carrier 74, itself carried on the pusher element68, exhibits a length sufficient to project distally beyond the stent 6and defines a lumen for the guidewire 20. In use, the guidewire 20extends along an axial path which lies side-by-side with the transfershaft 64 which is off the axis of the outer sheath 4. The proximal endof the distal marker carrier 74 is attached, conveniently by glue, tothe inner surface of the pusher element 68 to fix its axial position.The proximal end of the distal marker carrier 74 has a flared end orshows some sort of tulip-shape for undisturbed distal advancement of theguidewire 20 through the pusher assembly of the delivery system. Thefixing established by the glue and the flared end also reduces thelikelihood of separation of the carrier tube 74 from the pusher element68. The distal marker carrier 74 carries a distal marker, such as aradiopaque marker 72, indicating the position of the distal end of thestent.

[0082] The distal marker carrier 74 is a polymeric tube whereas thepusher element 68, the transfer shaft 64, the catheter shaft 66 and theconnection tube 78 are made of metal, conveniently stainless steel. Itis also conceivable to use other material combinations for these parts,such as nickel titanium shape memory alloy for the transfer shaft and acomposition of platinum/iridium (90/10) for the pusher element 68.

[0083] The distal marker 72 can be embedded or swaged into the distalmarker carrier 74 because the material used for the distal markercarrier 74 is relatively soft, preferably a resin tube.

[0084] Some applications require a thicker guidewire 20, such as a 35thou guidewire. In such cases, the distal marker carrier 74 may need tobe omitted, as shown in FIG. 6. The remaining structure of the pusherassembly can remain the same. Hence, the versatility of the pusherassembly is increased because of its usefulness with guidewires ofdifferent diameters.

[0085] Reverting to the embodiment shown in FIG. 5, however, a thickerguidewire can be accommodated if the distal marker 72 is moved to aposition just distal of the distal end of the compressed stent 6. Toresist bowing of the pushing wire 64, it can be bonded to an additionalshort length of tube mounted distally to the catheter shaft 66. Thebonding could be with glue. The mounting could be a telescopic mountingwithin the distal open end of the shaft 66, the tube length glued to thesaid distal end and extending, cantilevered, distal of the distal endwith the pushing wire glued to its outside cylindrical surface. Denialof bowing of the pushing wire within the lumen of the outer cathetershould eliminate any substantial “lost motion” when the outer catheteris initially pulled back proximally, and the pushing wire 64 goes intocompression, in the initial stages of stent release.

[0086] Drawing FIGS. 7, 8 and 9 show a third embodiment of the inventionwhich is, in some respects, a hybrid of the embodiments of FIGS. 5 and6.

[0087] In FIG. 7 there is an inner catheter 140 of polymeric material,glued inside the stainless steel shaft 116 and extending distally to adistal tip zone 142 which lies distal of the stent 6. Swaged around thisdistal tip zone is a distal marker 112, lying just distal of a distalend of the stent 6. For the remaining distal tip portion 142 of theinner catheter 140, lying distal of the distal marker 112, the diameteris slightly increased, as can best be seen in

[0088]FIG. 8, which increases the security with which the marker 112 isretained on the inner catheter shaft 140, with corresponding reducedlikelihood of loss of the marker 112 by slipping off the distal end ofthe catheter 140. As can be seen, the guidewire 20 extends through theshaft 116 and inner catheter 140, being a relatively snug fit withinthis lumen.

[0089] Lying on the outside cylindrical surface of the inner catheter140 is a transfer shaft 114 and connector 118. With a sequence of gluespots 144, the transfer shaft 114 is bonded to the inner catheter shaft140, thereby preventing any tendency for the transfer shaft 114 to bowwhen it is put in longitudinal compressive tension for release of thestent 6.

[0090] As shown in FIG. 8, at the distal end of the transfer shaft 14 isthe pusher 108 and this carries, on its outside cylindrical surface, anadditional thin platinum/iridium radiopaque marker band 146. A furthermarker 148 is integrated in the thickness of the outer catheter wall 4,just distal of the stent 6, overlying the marker 112 on the innercatheter 140. During progressive deployment of the stent, by proximalwithdrawal of the outer catheter 4, the radiologist will be able toobserve the progressive movement of the outer catheter marker 48,proximally away from the distal stent marker 112 and towards through andbeyond the proximal marker 146.

[0091] In the following, some of the advantages of the subject pusherassembly are elucidated.

[0092] Since the catheter shaft tube 116, the pusher element 108 and theguidewire 20 are all of metal, friction between the guidewire and thestent delivery system is low, and so PTFE or other special low-frictioncoatings can be omitted, thereby saving manufacturing costs.

[0093] During release of the stent, the transfer shaft remains under amore or less constant compressive strain once it has undergone a certainamount of bowing within the lumen of the outer catheter sheath 4 as aresult of the proximal withdrawal of the outer sheath. This bowingtypically reduces the distance between the pusher element 108 and thecatheter shaft 114 by approximately 5mm. The compressive strain sufferedby the transfer shaft 14 remains constant throughout the deployment ofthe stent for as long as the outer catheter 4 is in axial tension.Hence, a precise placement of the stent with respect to the stentingsite can be achieved and no significant “breathing”, as mentioned above,to be observed.

Industrial Applicability

[0094] In the following, some of the advantages of the present stentdelivery system, whether or not it has a rapid exchange configuration,are elucidated.

[0095] The present invention takes fully account of the previously knownadvantages of a rapid-exchange delivery system, such as easy removal andexchange of the delivery system, while the guidewire remains at adesired position within the patient's body.

[0096] The simplified internal structure of the distal portion of thedelivery system enables improved visualisation of the stenosis due anincreased volume flow of contrast fluid with each pulse.

[0097] Furthermore, during release of the stent, virtually no proximalmovement of the stent is seen, while the outer sheath is being withdrawnproximally. The present invention provides a metal structure all the wayfrom the proximal end of the pull back unit receiving the endwisecompressive force to the pusher element to keep the stent in placeduring stent deployment. Therefore, no bowing of the force transmittingcomponents is caused during stent release. Furthermore, the componentthat is withdrawn proximally, including the outer sheath 4, can alsoexhibit metal-to-metal connections end-to-end.

[0098] As shown in the illustrated embodiments, the length of thetransfer shaft, which preferably amounts to a maximum of 3cm, isrelatively short compared to its diameter, so that appreciable bowing issuppressed. In addition, the transfer shaft confined by the outer sheathand lying side-by-side to the guidewire inside the lumen of the outersheath has nowhere to go when it seeks to bend under compression duringstent release, thereby preventing shortening of the distance between thepusher element and the distal end of the rod. Hence, more preciseplacement of the stent with respect to the stenting site can beachieved. Furthermore, assembly of the system is facilitated andmanufacturing cost are reduced.

[0099] The system is further adaptable to guidewires of differentdiameters, which enhances the versatility of the system and itsacceptability to the practitioner.

[0100] It is worthwhile to mention that the delivery system may be usedin connection with a guiding catheter. The physician attempting to bringa stent to a stenosis site inside the patient's body uses an outer guidecatheter to be first introduced in the patient's body. Once the guidecatheter has been properly placed, a guidewire is introduced through theguide catheter lumen along which the delivery system is advanced to thesite of the stenosis in a next step. Here, the contrast fluid to be usedto visualise the stenosis can be injected, if the physician prefers todo so, through the gap between the internal surface of the guidecatheter and the external surface of the delivery system. Hence, theannulus between the pipe 18 and the rod 16 or tube, shown in FIG. 2, canbe further reduced in order to minimise the transverse dimension of thedelivery system, which is advantageous in terms of both, the recovery ofthe patient and the handling comfort for the physician.

[0101] Prior to use of the delivery system, as is the case for anydevices used to inject fluids into the human body, the delivery systemneeds to be vented and primed, i.e. the system is flushed with abiocompatible solution, such as a sodium chloride solution, until allthe air confined inside the system has been driven out of the system.The delivery system of the present invention may be flushed with such asolution from the distal tip of the delivery system prior to use. Thismay enhance the practical usefulness of the delivery system, since theguidewire is also inserted into the delivery system from the distal endof the system, so that the physician can carry out the flushing and theguidewire insertion almost in one go. This allows the physician tochoose the alternative with which he/she has grown most comfortable andwhich is best suited for the specific circumstances.

1. A pusher assembly for a delivery system for a self-expanding stent,the pusher assembly constituting a catheter shaft with a proximal pusherend to receive an end-wise compressive force and a distal pusher end (8)to deliver said force to a stent (6) to be delivered, the pusherassembly comprising: a pusher strand (16) extending from the proximalpusher end to a distal strand end which is nearer the distal pusher endthan the proximal pusher end; and a pusher element (8) which abuts thestent (6) in use to deliver said force to the stent; a transfer shaft(12) having a proximal end and a distal end, the proximal end beingconnected to the distal strand end and the distal end being connected tothe pusher element (8); the pusher element (8) defines a guidewire path,and said transfer shaft (12) lies to one side of said path.
 2. Assemblyas claimed in claim 1 wherein the transfer shaft (12) is welded to atleast one of the pusher element (8) and the pusher strand (16). 3.Assembly as claimed in claim 1 wherein the pusher element (8) is acylinder with a distal-facing end face to abut the proximal end of thestent (6).
 4. Assembly as claimed in claim 1 wherein the pusher element(8) is a radiopaque marker.
 5. Assembly as claimed in claim 1 furthercomprising a carrier tube and wherein the pusher element (8) surrounds acarrier tube (10) itself carried on the pusher element (8) andcantilevered distally from the pusher element (8) to lie in use withinthe lumen of a stent (6) to be delivered.
 6. Assembly as claimed inclaim 5 further comprising a radiopaque marker (26) on the carrier tubefor marking the distal end of the stent.
 7. Assembly as claimed in oneof claims 5 or 6 wherein a proximal portion of the carrier tube (10)extends proximally from the pusher element (8) and flares outwardlyproximally.
 8. Assembly as claimed in claim 1 in which the transfershaft (12) is present as two shaft portions joined by a connection piece(14).
 9. Assembly as claimed in claim 8 wherein the connection piece(14) is a collar.
 10. Assembly as claimed in one of claims 8 or 9wherein each of the transfer shaft portions is soldered to theconnection piece (14).
 11. A self-expanding stent deployment system foradvancement over a guidewire (2) and having a rapid exchangeconfiguration, comprising: a tubular sheath (4) defining a cavity withinwhich a stent (6) is confinable radially inwardly until deployment, thesheath (4) having a distal end and a proximal end and defining an axisof the system; a pipe (18) to pull the sheath (4) proximally to releasethe stent (6) and having a lumen to transport fluid (F) for delivery tothe sheath cavity; a pusher assembly including a pusher element (8) forabutting the stent (6) in use and a rod (16) for restraining the pusherelement (8) against proximal movement and extending from a proximal rodend proximally beyond the proximal end of the sheath (4) along the lumenof the pipe (18) to a distal rod end, the rod (16) being capable ofcarrying an endwise compressive stress (C) suffered by the pusherassembly during deployment of the stent (6); an adapter (20) defining atleast first (24) and second lumens (22) arranged side by side andparallel with the axis of the system and arranged to transmit forcesbetween the sheath (4) and the pipe (18), wherein the first lumen (24)is a guidewire (2) lumen, and the second lumen (22) communicates withthe lumen of the pipe (18) and with the sheath (4) cavity, and thesheath (4) having a tapered tip, distal of the stent (6) cavity whichenables the guidewire (2) to pass distally beyond the distal end of thesheath (4).
 12. The system according to claim 11, further comprising thepusher element (8) is a cylinder with a distal-facing end face to abutthe proximal end of the stent (6).
 13. The system according to claim 11wherein the pusher element (8) constitutes a radiopaque marker.
 14. Thesystem according to claim 11 further comprising a transfer shaft (12)which lies inside the sheath (4) to one side of the axis of the sheathand is arranged to transmit forces between the pusher element (8) andthe rod (16).
 15. The system according to claim 14, wherein the transfershaft (12) is welded to at least one of the pusher element (8) and therod (16).
 16. The system according to either one of claims 14 or 15,wherein the transfer shaft (12) comprises two shaft portions joined by aconnection piece (14).
 17. The system according to claim 16,characterised in that the connection piece (14) is a collar.
 18. Thesystem according to claim 16, characterised in that each of the transfershaft (12) portions is soldered to the connection piece (14).
 19. Thesystem according to claim 11 wherein the adapter (20) is made of metal.20. The system according to claim 11 wherein the connection between thesheath (4) and the adapter (20) is made by means of an adhesive.
 21. Thesystem according to claim 11 wherein the sheath (4) comprises anencapsulated metal braid (3).
 22. The system according to claim 21further comprising metal studs (20A) disposed around the circumferentialsurface of the distal end of the adapter (20), the studs cooperativelyengaging the metal braid (3).
 23. The system according to claim 11wherein the first lumen (24) is defined by two arcuate segments (23A)and (23B).
 24. The system according to claim 11 wherein the pipe (18) isinserted into the first lumen (24) of the adapter (20) until it abuts anend face of a recess provided on the defining walls of the first lumen(24).
 25. The system according to claim 11 further comprising a carriertube and wherein the pusher element (8) surrounds the carrier tube (10)itself carried on the pusher element (8) and cantilevered distally fromthe pusher element (8) to lie in use within the lumen of the stent (6)to be delivered.
 26. The system according to claim 25 wherein thecarrier tube (10) itself carries a radiopaque marker (26) for the distalend of the stent (6).
 27. The system according to claim 23 wherein aproximal portion of the carrier tube (10) extends proximally from thepusher element (8) and flares outwardly proximally.
 28. As assembly asdefined in claim 11 further comprising, in combination, a stentcontained within the distal region of the sheath in a compressedconfiguration.
 29. A process for assembling a self-expanding stent and adelivery device for the stent comprising: providing a sheath dimensionedto contain a self-expanding stent in a compressed configuration smallerin diameter than that to which the stent may expand when released fromthe sheath; a proximal tubular member connected to the proximal end ofthe sheath; a proximal pusher strand disposed within the proximaltubular member, the pusher strand having a proximal end and a distalend; providing a transfer shaft having a proximal end and a distal end,the length of the transfer shaft being selected with respect to thelength of the sheath and the stent such that when the stent is containedwithin the distal portion of the sheath, the transfer shaft will extendfrom the distal end of the pusher strand to the region immediatelyadjacent the proximal end of the stent; connecting the proximal end ofthe selected transfer shaft to the distal end of the pusher strand; thedistal end of the transfer shaft having a pusher element attachedthereto, the pusher element defining a guidewire path and being adaptedto engage the proximal end of a stent contained within the sheath; thetransfer shaft being disposed to one side of the guidewire path; andplacing a stent within the distal portion of the sheath.
 30. A cathetercomprising a proximal shaft portion and a distal shaft portion attachedto the proximal shaft portion, and means to stiffen the catheter at thejunction between the proximal shaft portion and the distal shaftportion; the catheter having a guidewire opening located a substantialdistance distally of the proximal end of the catheter for rapid exchangeof the catheter over a guidewire.
 31. A catheter as defined in claim 30wherein the guidewire opening is provided by an opening in the means tostiffen the catheter.
 32. A catheter as defined in claim 31 wherein themeans to stiffen the catheter comprises a mounting piece for attachingthe distal shaft portion to the proximal shaft portion.
 33. A catheteras defined in claim 31 wherein the guidewire opening faces in adirection substantially parallel to the longitudinal axis of thecatheter.
 34. A catheter as defined in claim 31 further comprising meansto guide passage of a guidewire through the guidewire opening in thecatheter.